In a process for preparing polyethylene terephthalate (referred to as PET hereinafter), bis(2-hydroxyethyl) terephthalate (referred to as BHET hereinafter) having Formula (1) below is prepared, followed by polycondensation of BHET to prepare PET.

In the industry, BHET may be prepared by subjecting ethylene oxide and terephthalic acid to a reaction so as to avoid problems encountered in a transesterification process in which methanol is produced as an undesirable byproduct and problems encountered in an esterification process which requires a pressurized atmosphere and addition of a significant amount of glycol, and which results in a product containing undesirable oligomer.
U.S. Pat. No. 3,052,711 discloses a process for the preparation of di(β-hydoxyethyl) terephthalate (i.e., BHET) by the reaction of ethylene oxide with terephthalic acid. A reaction mass is formed by continuously feeding ethylene oxide and a slurry prepared from terephthalic acid, water, and a water-soluble base into one end of a heated reaction zone. Possibility of production of glycol by the reaction of water with ethylene oxide may be reduced, and the problem of hydrolysis of BHET may be avoided. However, a waste solvent which has to be further processed is in an amount of about 1 kg per kg of BHET.
U.S. Pat. No. 7,332,548 discloses a process to produce a partially esterified carboxylic acid product, which comprises contacting at least one di carboxylic acid with at least one alkylene oxide in a reactor zone in the presence of at least one solvent and at least one basic catalyst. The solvent includes at least one selected from toluene and xylene. However, as shown in Table 5, conversion of esterified terephthalic acid is below 54.4%.
U.S. Pat. No. 6,310,233 discloses a process for reacting dicarboxylic acid with alkylene oxide to produce hydroxyalkyl ester monomers and perhaps minor amounts of oligomers, A mixture of water with dimethyl ether is used as a solvent in the process. However, a primary product produced in the process is mono(2-hydroxyethyl) terephthalate of Formula (2), rather than BHET.
